10/08/2015 Forces and Motion

What is motion? In Physics, motion is referred to as the movement of an object in relation to time and its reference point Write down 5 examples of motion 10/08/2015

Physical Challenge!!! Teams of 3-4. Build a structure using newspaper and tape that can do the following: Allows a marble to have the slowest average speed while in the structure AND Allows a marble to have the fastest average speed over 3m when it leaves the structure AND Hits a target 3m away (a coke can) 10/08/2015

Distance, Speed and Time Speed = distance (in metres) time (in seconds) V= d tSpeed is measured in meters per second (ms -1 ) d tV

What is speed? How fast an object is moving over a distance over time. What two variables are needed? Distance Time 10/08/2015

Measuring speed In a group of 3-4 designate: A runner A timer A recorder A organiser What to do: 1. Get your runner to run 50m. Record the time. 2. Run a set distance (set by me) at the same pace they ran the 50m. Record the time taken 3. Run a set distance at the same pace as above. Record the distance 10/08/2015

What is speed? Speed (v) is calculated using the distance an object travels divided by the time it takes to travel that distance. Instantaneous speed is the actual speed at any moment. The average speed is the speed over part or all of a journey.

10/08/2015 Distance, Speed and Time Speed = distance (in metres) time (in seconds) V= d tSpeed is measured in meters per second (ms -1 ) d tV

10/08/2015 Speed vs. Velocity Speed is simply how fast you are travelling… Velocity is “speed in a given direction”… This car is travelling at a speed of 20m/s This car is travelling at a velocity of 20m/s east

10/08/2015 An example to copy… A car travels 600 m in 20 s, what is its average speed? ALWAYS 1. give the formula V = d/t 2. show the working= 600 m / 20 s 3. Give the answer and the units 4. Round if necessary to 2DP = 30 ms -1

Try these 1. A car travels 100 meters in 5 seconds. Calculate the cars speed. 2. A boy runs 200 meters in 20 seconds. Calculate the boys speed. 3. A plane travels 3000 meters in 6 seconds. 10/08/2015

Speed units- they can change The way we measure speed can depend on how fast the object is moving. What units are distance and time being recorded in below? 112 km/h10000 cm/s 65 m/h12 m/min 76 km/s 10/08/2015

Speed units can be decieving…. Which object is travelling faster? A. 100 m/s B. 36 km/h 10/08/2015

Some problems to try….. 1.Alexandr Vinokurov (KAZ) won the mens road race (249.5Km) in Hours. Find his average speed in Km/h 2. Linda Melanie Villumsen (NZ) came fourth in the women road race covering 29Km in 37:59.18 minutes. Calculate her average speed. 3. The Kiwi’s Cohen and Sullivan won the rowing double skulls final covering 2000m in min. Calculate their average speed. 4. Compare their speeds over the 3 rd 500m ( min) with the final 500m ( min). 5. Allison Schmitt (USA) won the 200m freestyle in min. Calculate her average speed.

Think about these scenarios What will change in the following situations (either speed, distance or time will increase or decrease) 1. a car takes longer to travel 100m 2. a car moved at a faster speed 3. a car travelled at 50 km/h over 500m then 1000m- which one will take longer to cover? 10/08/2015

Distance-time graphs ) Diagonal line downwards = 3) Steeper diagonal line = 1)Diagonal line = 2) Horizontal line = Distance (metres) Time/s

10/08/ )What is the speed during the first 20 seconds? 2)How far is the object from the start after 60 seconds? 3)What is the speed during the last 40 seconds? 4)When was the object travelling the fastest? Distance (metres) Time/s

How would you show acceleration? 10/08/2015

Keywords to know: Constant speed Acceleration Speed Stationary Rate of distance over time Change in speed over time Not moving Covering the same distance over time 10/08/2015

Making darts Task: to design two darts. 1. a dart that can cover 5m with the fastest speed. 2. a dart that can cover 3m with the slowest speed. You dart must only be made out of paper, paper clips and tape. You must make two results table to record each trial and final speed. 10/08/2015 DistanceTimeAverage speed

Review Questions 1. Calculate the speed of a car covering 120m in 5 seconds. 2. Calculate the distance a bike travels if it takes 12 seconds and moves at a speed of 4m/s. 3. Calculate the time it takes a person to run 50m at a speed of 3 m/s 4. Draw a simple distance vs time graph to show the journey below: a. A car accelerates to a speed of 20m/s over 5 seconds. B. the car travels at a constant speed of 20 m/s for 10 seconds. C. The car accelerates for 3 seconds to 35 m/s 10/08/2015

Acceleration 1. Get out your car app 2. In your car start from a stationary position and accelerate for 10 seconds. 3. record down your speed. 4. how could you calculate acceleration (what variables do you have?). 10/08/2015

Acceleration ΔVΔV Δ T A Acceleration = change in velocity (in ms -1 ) (in ms -2 ) time taken (in s) Acceleration measures the rate that speed changes over time. e.g When a car starts increasing in speed from a stop sign, we say that it is accelerating. Acceleration is an increase in speed over time. Deceleration is a decrease in speed over time. The unit for acceleration is ms -2. This means meter per second per second! E.g a car accelerating at 2 ms -2 is increasing its speed by 2 meters per second every second it travels.

Examples 10/08/2015

Velocity-time graphs Velocity ms -1 T/s 1) Upwards line = 2) Horizontal line = 3) Upwards line = 4) Downward line =

10/08/ )How fast was the object going after 10 seconds? 2)What is the acceleration from 20 to 30 seconds? 3)What was the deceleration from 30 to 50s? 4)How far did the object travel altogether? Velocity ms -1 T/s

10/08/2015 Distance-time graph for non-uniform motion Distance (metres) Time/s Object is accelerating up to here Object is now decelerating

10/08/2015 Velocity-time graph for non-uniform motion Speed (m/s) Time/s Object’s acceleration is increasing Object’s acceleration is decreasing

Calculating acceleration Collect data so you can calculate two different rates of acceleration from your object. Spend 5 minutes discussing how you will do this. You must take some evidence (photo, video) to show your data gathering. You must describe and explain several variables you controlled to make your results accurate. You must show you working to calculate the two acceleration values. 10/08/2015

Car journey app 1. Copy the simple journey graphs into your book 2. Complete the journeys on the board using your car app. 3. Underneath each graph describe your motion through the journey. 10/08/2015

Calculating acceleration of a point in your journey To be done in pairs: Timer/ odometer reader Racer What to do: calculate the rates of acceleration below: 1.From a stationary position accelerate (at max) for 5 seconds. Record the odometer reading and calculate. 2.From a speed of 40km/h accelerate slowly for 10 seconds 3.From a speed of 80km/h accelerate fast for 5 seconds 4.Make your own one up What units will you use for acceleration? 10/08/2015

What is causing the car to accelerate? 10/08/2015

What is a force? A force is a “push” or a “pull” that can act on an object. Some common examples: ________ – pulls things downwards ___ ________ (drag) – acts against anything moving through air ______ – keeps things afloat _____ – acts against anything moving Words – upthrust, air resistance, friction, weight

What happens to an object when forces are applied? Accelerate (speed up or slow down) Change direction Change shape 10/08/2015

Balanced and unbalanced forces Consider a camel standing on a road. What forces are acting on it? Weight support These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.

10/08/2015 Balanced and unbalanced forces What would happen if we took the road away? Weight support

10/08/2015 Balanced and unbalanced forces What would happen if we took the road away? The camel’s weight is no longer balanced by anything, so the camel falls downwards… Weight

10/08/2015 What would happen if we took the road away? The camel’s weight is no longer balanced by anything, so the camel falls downwards… Balanced and unbalanced forces

10/08/2015 Balanced and unbalanced forces 1) This animal is either ________ or moving with _____ _____… 2) This animal is getting _________… 3) This animal is getting _______….

10/08/2015 Balanced and unbalanced forces

Acceleration due to gravity When an object is in free fall it will accelerate due to gravity at 10ms-2. When objects fall from a large height they do not continue to accelerate but eventually reach a constant speed. This speed is called terminal velocity. This occurs because eventually air resistance will be evenly balanced with gravity. What will happen in the following scenarios? A. a coin and a feather are dropped, they have the same mass. B. two coins are dropped, one is heavier but both have the same surface area. 10/08/2015

Newton’s laws 1. When forces acting on an object are balanced the object will either be stationary or moving at a constant speed. 2. The larger the mass the more force is needed for the object to accelerate. 3. For every force there is a reaction force. 10/08/2015

What different forces are there? Frictional Force Weight Force Tension Force Electrical Force Support Force Magnetic Force Air Resistance Force Applied Force Spring Force Write down examples where you might see these forces being applied. 10/08/2015

Drawing force diagrams Forces must be drawn in pairs Arrows must be touching the object Arrow size must be a reflection of the force being applied e.g. If forces are balanced the arrows must be the same length If the forces are unbalanced the arrows must be different sizes Named examples of forces must be given 10/08/2015

Net Force If all the paired forces were added up then the sum or total force is called the Net force 10/08/2015

Force and acceleration If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers: Force (in N) = Mass (in kg) x Acceleration (in m/s 2 ) F aM

10/08/2015 Force, mass and acceleration 1)A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? 2)A force of 3000N acts on a car to make it accelerate by 1.5m/s 2. How heavy is the car? 3)A car accelerates at a rate of 5m/s 2. If it weighs 500kg how much driving force is the engine applying? 4)A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? F aM

To discuss properties of forces Unistructual I can communicate one idea about forces Multistruct ual I can communicate several ideas about forces Relational I can communicate several ideas about forces AND Explain how they are linked together Extended Abstract I can communicate several ideas about forces AND Explain how they are linked together AND I can make a generalisation about forces

Discussing the journey of an object 1. Name all forces acting on the object (name them in pairs) 2. describe the strength of the forces and the direction that they occur 3. describe if the forces are balanced or unbalanced 4. Explain the net force 5. Describe the motion of the object as a result of the forces and the direction 10/08/2015

Mass vs Weight Mass is the amount of matter an object has. This is measured in Kg’s Weight is the force of gravity acting on a mass. This is measured in Newtons! This can be calculated by: Weight= F gravity = mass X gravity »Where gravity is 10N Kg -1 »What does that mean? 10/08/2015

Why is g= 10Nkg -1 ? Gravity will apply 10N of force on an object for every Kg of mass it contains. Why? Gravity is a force When an object is dropped only gravity is acting on the object The force(s) are unbalanced (what do objects do?) Gravity causes objects to accelerate at 10ms -2 Find the force of these objects: 1. an object falls with a mass of 12 Kg. 2. an objects falls with a mass of 26Kg So all you need to do is multiply the mass by 10 10/08/2015

Helicopter investigation Design an experiment to investigate acceleration due to gravity. You have access to: 1m ruler Paper clips Helicopter Stop watch (on your phone) Electronic Scales You must record some data You must change an independent variable with a range of 3 You must repeat 3 times 10/08/2015

Review Questions 1. Define the term weight 2. Define the term mass 3. Compare the units they are measure in. 4. g=10NKg -1. Write a sentence to describe what this means. 5. two objects are dropped. One has a mass of 2kg and the other a mass of 42Kg. Calculate the force of each. 6. Ignoring drag/air resistance. Which object would hit the ground first? Why? 10/08/2015

Aussie Science competition- Tomorrow start of P3 -allocated one hour -only use pencils -eraser -calculator -ruler 10/08/2015

Mass and Weight

MASS Mass is the amount of matter in an object. Mass is measured in kilograms (kg). Mass is constant anywhere in the universe. For the mass of an object to change it must lose or gain matter.

weight Weight is the force of gravity acting on a mass. Weight is measured in Newtons (N). Larger gravity means larger weight force. On earth a one kg mass has a weight of 10N on Earth.

Alien Gravity My mass is 50kg. If gravity on Earth is 10m/s 2, what is my weight? Weight = mass x gravity = _______kg x ______m/s 2 = ________ N Weight = mass x gravity = _______kg x ______m/s 2 = ________ N Use the boxes to help you work out the weight of the alien. My mass is still 50kg. But how much do I weigh here? Weight = mass x gravity = _______kg x _____N/kg = ________ N Weight = mass x gravity = _______kg x _____N/kg = ________ N Gravity = 30N/kg = 30Nkg -1 Weight = mass x gravity = 50 kg x 10 m/s 2 = 500 N Weight = mass x gravity = 50 kg x 10 m/s 2 = 500 N Weight = mass x gravity = 50 kg x 30 N/kg = 1500 N Weight = mass x gravity = 50 kg x 30 N/kg = 1500 N

More Alien Gravity g = 12 m/s 2 My mass is ALWAYS 50kg, but what is my weight on this planet? On this small moon I only weigh 75N. I wonder what the gravity is? Gravity = _______ / ________ = _______N / ______kg = ________ m/s 2 Gravity = _______ / ________ = _______N / ______kg = ________ m/s 2 Weight = mass x gravity = 50 kg x 12 m/s 2 = 600 N Weight = mass x gravity = 50 kg x 12 m/s 2 = 600 N Gravity = weight / mass = 75 N / 50 kg = 1.5 m/s 2 Gravity = weight / mass = 75 N / 50 kg = 1.5 m/s 2

More Alien Gravity Hint :- Use the weight and mass of the first alien to find the gravity of the planet. Then use that to find the mass of his brother. Hint :- Use the weight and mass of the first alien to find the gravity of the planet. Then use that to find the mass of his brother. On this planet, I weigh 750N. My brother weighs 600N. What’s my mass? Gravity = weight / mass = 750 N / 50 kg = 15 m/s 2 Mass = weight / gravity = 600 N / 15 m/s 2 = 40kg Gravity = weight / mass = 750 N / 50 kg = 15 m/s 2 Mass = weight / gravity = 600 N / 15 m/s 2 = 40kg

Fun with Eggs Oh nooooooooooo!!!!! An egg has been dropped from a height of 3m. Design a safety parachute for your own egg. Specs: Must have a parachute At least half of the egg must be visible at the end of the drop. Winning criteria: Non-cracked egg Lowest WEIGHT Slowest time to fall 3m. 10/08/2015

Balloon Experiment 1. Why can 1 person lie down on several balloons but couldn’t stand? 2. What happened to the balloon shape when a person was lying on them? What about when more people were added? 3. Why was it harder to sit on balloons when the cardboard was removed? 4. Where did the balloons need to be placed (relative to the body)? Why? 10/08/2015

Pressure Pressure is a measure of how much force is pushing on a certain area. It can be calculated by: P=F/A The unit for pressure is Pascals (Pa), but the measurements are often large so kPa are common (KiloPascal) 1 pascal (Pa) is a pressure of 1 newton per square metre 10/08/2015 F AP Pressure (in Pa) = Force (in N) / Area (in m 2 )

Find the pressure on your feet 1. Trace one of your feet. 2. Count the number of cm Convert into m Find your mass. 5. Convert to weight force. 6. Calculate pressure. Remember you have two feet! 10/08/2015

Explaining pressure Use the variables in the formula for pressure to explain what is happening. E.g if a person stands on two feet and tries to balance on one foot how would the pressure on the one foot change? 1. Has the area changed? 2. Has the force changed? 3. Has the pressure changed as a result? 10/08/2015

Friction Friction is the force which opposes one surface moving (or trying to) over another. Heat is often produced as a result of friction (due to energy conservation). 10/08/2015

Uses of friction Where friction is useful: Tyres Brakes Shoes (sprigs) Snow chains Where friction is not useful: Car engines Car transmission Ice skates 10/08/2015

Stopping a car… Braking distance Too much alcohol Thinking distance Tiredness Too many drugs Wet roads Driving too fast Tyres/brakes worn out Icy roads Poor visibility